Choice of a particular type of drilling fluid depends on the subterranean formation characteristics, including geologic formations and mineralogy, borehole stability requirements, presence of any abnormal pressure zones in the formation, and any need to prevent underground water pollution. Whenever one of such existing conditions changes, then the entire fluid system may have to be modified based on the new conditions. Such changes in the fluid system are expensive and time-consuming. Moreover, the fluid system that may properly solve an encountered problem may be less than optimum for the rest of the drilling column.
Mud rheology plays a fundamental role in drilling oil and gas wells. If the rheology of the fluid is not appropriate for the formation and physical conditions of the well, the drilling operations may be spoiled with drilling problems such as lost circulation, poor hole cleaning, fracturing phenomena of the crossed formations, and stuck pipe, for example. Some of the main drilling parameters involved are cutting, lifting and hole cleaning efficiencies, resulting both from variation of the velocity profile of the fluid flow, and from variation of the rheological parameters, and the pressure spatial distribution along the well profile. It is extremely important for the drilling fluid to be able to transport cuttings up to the well surface without any restriction in any of the existing annulus sections. Such unrestricted transport depends on many parameters including the geometry of the annulus section, the rotation velocity of the drill string, the rate of drill bit penetration into the formation, the flow rate of the drilling fluid, the cuttings characteristics, and above all the rheology of the used drilling fluid. It is very important to keep a constant limit on the concentration values of the cuttings during the cuttings transport to avoid solid particle deposition inside the well, risking problems of borehole occlusion, bit balling, and drill string sticking during the drilling process.
Although the efficiency of a number of different drilling fluids in transporting cuttings has been reported at values up to 80%, new technical problems arise when drilling deep water and ultradeep wells. Such problems are compounded when the effects of high pressure and temperature are considered. High temperatures can heavily alter and sometimes reduce the viscosity of a drilling mud or a completion fluid and can enhance the speed of chemical reactions within such mud or fluid. These consequences can in turn result in other consequences such as increased dispersion or flocculation of the mud solids with resultant increase in fluid loss properties and change in the thickness of the mud cake.
Optimum drilling mud is therefore essential to control the pressure of the well, provide lubrication and cooling, and for transport of drilled out material. Different muds are needed for different conditions, depending on several factors, resulting in mud of specific properties for specific conditions. The best known parameters characterizing mud are viscosity and density. The mud can be based on water, or mineral, or hydrocarbon oil, and can include traditional materials like bentonite clays or other natural materials or synthetic materials. The selection and formulation of the mud is managed by the mud engineer.
It is industry practice to monitor the properties of the mud returning from the well. This is essential in order to detect traces of hydrocarbons, particularly traces of gas, which can give an early warning of a gas kick or uncontrolled pressure rise. However, with respect to the mud to be pumped down into the well by the mud pumps, it is industry practice to take manual samples in order to ensure that the mud properties are as intended. The sample must typically be sent to a laboratory, either on the drilling rig or on land at a remote location, and the process of analyzing may take considerable time. For drilling operations offshore, time is very expensive, and even a moderate reduction in wasted time can have a significant impact on the economy of the operation. Another aspect is the increased safety if it could be ensured at all times that only mud having the correct properties is pumped down the drill string.
Managing drilling fluid properties at the rig site is a critical step to delivering every well successfully. Fluctuations in these properties, however are inevitable, and even minor deviations in the drilling fluid can have dramatic impacts on wellbore stability, hole cleaning, equivalent circulating density (ECD), and overall drilling performance. Hydraulic simulations are an essential part of planning the drilling program, and real-time data can offer greater opportunities to improve overall operations.
Many technologies exist for data acquisition and processing of data. Many technologies exists for collecting samples of mud coming up from the well, and some for collecting samples of mud as mixed and to be pumped down the drill string. In addition, many technologies exist for analyzing single parameters of the mud.
However, a demand still exists for technology in order to reduce the time spent for monitoring the mud properties, provide continuous monitoring, provide data for more parameters than current industry standard practice, reduce the risk of pumping incorrect mud composition, reduce waste, tankage requirement, and ineffective drilling unit time and increase safety. The objective of the present invention is to meet the demand.